5v fan from 12V power supply or Sanguinololu

I was going to use an ATX supply but found that it had issues so I picked up a 12V 30A supply that seem to be common for repraps. I want to run PLA so I want to keep the PEEK tube cool to provent issues. The fan I was planning to use is a 5V fan (grabbed it from the junk pile so the price was right). It says 5V 0.14A on the label. I figure I've got two choices:

1. Pick off 5V from the Sanguinololu board which does have a VR to get 5V. But is there enough extra current for a small fan? Where is the best place to wire it up?

2. Use a resitor to drop the voltage down to 5V for the fan. If my math serves me correctly it seems like 50 ohms would be correct at about 1W which seems like a bit of a waste. Maybe I could scrounge up a cheap VR or find a different fan, but it needs to be a really small fan to fit close to the J-head and cool the PEEK without the tip (even with a duct).

Is there a good place on teh Sanguinololu to pull a steady 5V? Can it drive that much extra current (especially if I wire the heat bed up separately as described in another thread)?

Thanks,
Bret

Edited 1 time(s). Last edit at 03/20/2013 01:01AM by cobrageek.

I may have just answered my own question. I looked at the wiki page for the Sanguinololu and it looks like on the Aux connections, the second pair in (counting from the Z-stop connector) is a +5V and ground connection point. Assuming I understand correctly the connection for the SD card setup, it even looks like that will still work if I use this connection point to power a fan.

The next question is can it really drive that much extra current without it causing any problems. It's only 0.14A, but there's always a straw for every camel's back.

One thought along these lines that I saw suggested in another thread leads to the following questions about the end stops:

From the schematics it looks like they can either be 5V or 12V, but I can't find the "jumper" (SJ100) that seems to control the voltage choice. Where is this jumper? What is the "normal" choice here? Does it matter?

Are the end stop switches wired normally open or normally closed? Is it configurable?

Here's the thinking. If the Z-stop switch is wired normally closed, then one could (maybe) wire that switch in series with this hot end fan so that the fan was only on when the Z-axis was off the stop. Does this even make sense?

Thanks for the experienced input.

i run my both fans on sangluino from a extra cable from my ATX power supply,
i don't see why you could not do that as well, but use the 5v instead of the 12v.
it's for a fan, it's not that it has to be 5V death on.

cobrageek Wrote:
-------------------------------------------------------
> Is there a good place on teh Sanguinololu to pull
> a steady 5V? Can it drive that much extra current
> (especially if I wire the heat bed up separately
> as described in another thread)?

I would avoid doing this because brushless fans pull a square waveform of current and wiring such a fan directly to the same supply that the microcontroller uses is just asking for interference... I would use a completely separate 5V supply or failing that, feeding the fan thru a 12->5V regulator or even a suitable resistor from 12V rail would be the next best option.

Possenier, my plan was to use the 5V from the ATX supply, but it turns out that supply had issues so I bought a 12V only supply (30A) that is a smaller form factor. That means I have no 5V supply other than the Sanguinololu.

ttsalo, I was afraid of exactly that. I know motors can create considerable noise and I didn't want to mess up the electronics. I'll consider the resistor approach but wasn't sure how hot it would get (and it does seem like a waste of power). I'll poke around to see if I can get a 12-->5 VR from the scrap heap or maybe a 12V to use (but the smallest fans seem to be 5V). Maybe I'll look at nophead's fan controller hack while I'm at it.

I've come up with a couple of good options I think:

1. I have a cheap USB car adapter that I bought for my iphone but doesn't work with apple products (cheap). I could rip it apart and use the 12V-->5V converter and just wire it from the 12V supply to run the fan.

2. I've seen a lot of people who run fans blowing right below the nozzle to help with overhangs. I have a second one of these fans and I could run it in series with the first so each would be seeing 6V which would probably work just fine. It doesn't provide any adjustability in case I have issues of it cooling too fast sometimes, but I could adjust the ducting if needed I suppose.

Any opinions on option 2? Would a focused 20mm fan be useful to cool the PLA and help overhangs or is it not powerful enough?

You could just get a $2 7805 regulator and hook up the 12V and get 5V out. No need for filtering or anything for fans. They will handle a 1A load so that's not an issue.

The 7805 is a good idea. I checked through my surpluss parts but I don't have any laying around. But I do have the car USB adapter that I'm never going to use and it was easy to break open. It's more sofisticated than I need, but it's free and will do the trick so I'll probably go that direction. I'm sure I could wire a second fan off of it as well if I decide it's needed later on.

Thanks for the helpful ideas.